Teach lesson
The PV constant challenge
Use five real pressure-volume pairs to decide whether one multiplication rule remains consistent throughout a full syringe compression.
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Learning Outcomes
Collect five selected pressure-volume pairs from the 60 mL run.
Calculate PV in consistent units for each selected pair.
Judge whether PV is approximately constant using a clearly defined deviation criterion.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Can multiplication reveal a pattern?
6 min
A compressed syringe produces many different pressure-volume pairs. At first they can look like an untidy collection of numbers. One operation may reveal a hidden regularity: multiply each pressure by its volume.
For a fixed amount of gas at approximately constant temperature, Boyle's law proposes that PV should stay approximately constant:
The rule you will test
P\,V \approx \text{constant}
The displayed pressure is absolute pressure; do not add atmospheric pressure. Keep the measured pressures within this sensor’s specified 0–210 kPa range. Values above that range cannot be used to test the physical model. The syringe scale also omits the small volume of gas in the tubing and sensor.
Before calculating, what do you expect the five PV products to do?
Collect five pairs and calculate PV
16 min
Use the 60 mL syringe, trial 1. Record five volumes in order: 60, 50, 40, 35 and 30 mL. Continue through the other pauses without adding rows. Stop collecting at 30 mL so the selected pressures remain within the specified sensor range.
Evidence comes from this display
Read the large pressure number beside kPa; it appears red in the current interface. If it uses a decimal comma, enter a decimal point in numeric fields.
Lab-screen note: the introduction may mention pressure and temperature. In this Boyle run, syringe volume changes, pressure is measured, and temperature is treated as approximately constant.
Open the 60 mL run
Open the lab and select the 60 mL syringe, trial 1.
Before compressing, record the initial pressure at 60 mL.
Use the 5 mL decrease control. At the pauses for 50, 40, 35 and 30 mL, copy the displayed pressure in kPa; pass through other pauses without adding rows.
Stop collecting at 30 mL. If a selected reading exceeds 210 kPa, flag it as outside the sensor range.
Calculate each PV product. Replay an unclear pause or describe the uncertainty in the note column; never replace a reading with an ideal number.
The five rows are already identified. Use the pressure as displayed and round each PV product to the nearest 0.1 kPa·mL. Leave the percentage-deviation column blank until you calculate the mean in the next phase; the table is completed in two stages. The optional note can be used to mark a difficult reading, such as a blurred digit or fluctuating display. Leave any extra interface row unused.
Five tests of PV
First copy the pressure and calculate PV. After finding the mean PV, complete the percentage deviation for every row.
| Volume mL | Pressure kPa | PV kPa·mL | Deviation from mean PV % | Reading note |
|---|---|---|---|---|
Decide what ‘constant’ can mean
8 min
An experimental constant does not require identical products. First calculate mean PV = sum of five PV products ÷ 5, using the products already rounded to 0.1 kPa·mL. Then complete the table's final numeric column with percentage deviation = |PV − mean PV| ÷ mean PV × 100, rounded to 0.1%. For this lesson, call a row a noticeable deviation when its percentage deviation exceeds 5%. This is a transparent classroom rule, not a universal law of nature.
Calculate the mean of your five PV products. Enter it rounded to 0.1 kPa·mL and show the sum divided by five.
How many of your five rows have a percentage deviation that exceeds 5%? Choose the one count that matches your completed table.
Which row has the largest percentage deviation from the mean PV? State its volume, PV, and percentage, then apply the 5% rule. If it is a noticeable deviation, give one possible cause related to the measurement or setup—such as a difficult reading, temperature change, leak, sensor response, or uncounted setup volume—without claiming that cause is proven.
Give the challenge verdict
5 min
Write a four-sentence verdict:
- Decide whether the run supports approximately constant
PV. - Cite at least two
PVproducts from your table. - Report how many rows exceed 5% deviation and identify the row with the largest deviation.
- Explain how the full data set supports or limits your verdict; do not present a possible cause of the deviation as proven.
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